Law of dilution

Ostwald’s law of dilution relates a weak electrolyte’s degree of ionization to its concentration and dissociation constant, predicting greater ionization at lower concentrations.

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Ostwald’s dilution law equation: For a binary weak electrolyte, the dissociation constant is K = cα²/(1−α), where c is concentration and α is degree of ionization. This equation states the law quantitatively and shows how concentration governs ionization.
Chemical equilibrium: A dynamic state in which forward and reverse reactions proceed at equal rates. Weak-electrolyte ionization is an equilibrium rather than a one-way conversion.
Strong electrolyte: An electrolyte that is nearly fully ionized in solution over a broad concentration range. Its near-complete ionization makes the law’s weak-dissociation approximation unsuitable.
Wilhelm Ostwald: A German chemist who helped establish physical chemistry and received the 1909 Nobel Prize in Chemistry. He formulated the dilution relation for weak electrolytes.
Degree of ionization: The fraction of dissolved electrolyte units that exist as ions in solution. This is the quantity the law predicts as concentration changes.
Electrolyte: A substance that produces mobile ions when dissolved or molten, enabling electrical conduction. The law concerns electrolytes whose ionization is incomplete in solution.
Debye–Hückel theory: A theory that estimates ionic activity coefficients in dilute electrolyte solutions from electrostatic interactions. It accounts for nonideal ionic interactions that simple dilution-law treatments neglect.
Arrhenius: A Swedish chemist whose theory of electrolytic dissociation explained ion formation in aqueous solutions. His dissociation theory supplied the framework Ostwald’s relation quantified.
Dissociation constant: An equilibrium constant that measures the extent to which a substance dissociates into products. It sets the equilibrium strength used to relate concentration and ionization.
Weak electrolyte: An electrolyte that only partially ionizes in solution under ordinary conditions. Partial ionization is the defining condition for the law’s simple treatment.